Perceptual dithering for octave subband image coding

Octave subband coding has been used as an efficient image coding approach for various well-known standards such as MPEG-4 and JPEG-2000. Although the sub-images in the octave subband representation have low statistical correlation, the visual similarity among the sub-images indicates that there exists some unexploited perceptual redundancy between sibling bands in addition to the parent–child redundancy. In this paper, we show that the original image can be perceptually dithered to form a visually equivalent image with increased interband correlation that can be used to achieve more compression. To remove the redundancy among the sibling subbands of an image, we provide a novel perceptual dithering approach that is based on entropy reduction technique with perceptual model. The theoretical basis for the entropy reduction is proven by a theorem for Gaussian distributed signals. The use of our dithering technique is demonstrated for an MPEG-4 compliant encoder with improved coding efficiency using MPEG-4 Visual Texture Coding (VTC) based on zerotree entropy coding. Our results show that there exists a perceptual interband redundancy even though the original interband correlation is small. For a perceptually transparent image quality, our approach can achieve bit savings over MPEG-4 VTC by 11–30% while maintaining compatibility with the MPEG-4 standards. 2003 Elsevier Inc. All rights reserved. This work was supported by the National Science Council, Taiwan, ROC under the Contract NSC 91-2218-E009-014. * Corresponding author. Fax: +886-3-5724176. E-mail addresses: [email protected], [email protected] (C.-M. Liu). 1 Tihao Chiang is currently an Associate Professor and Chung-Neng Wang is a research fellow of the Department and Institute of Electronics Engineering, NCTU, Taiwan. 2 Chi-Min Liu is currently a Professor of the Department and Institute of Computer Science and Information Engineering, NCTU, Taiwan. 1047-3203/$ see front matter 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.jvcir.2003.07.003 164 C.-N. Wang et al. / J. Vis. Commun. Image R. 15 (2004) 163–184